The inner workings of a Sprint 4G LTE cell site (pictures)

CNET goes behind the scenes at a Sprint cell site in San Francisco, as the carrier prepares to officially launch its 4G LTE network in the Bay Area.

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Sprint's LTE cell site

Although Sprint's 4G LTE network has already been available in some pockets of San Francisco for months, the carrier has yet to announce its official launching. Until then, CNET takes a look at one of the carrier's active cell sites in San Francisco, known as Site SF33XC664.

Going down Van Ness

The site is located on the roof of the Medical Arts Building on Van Ness Avenue. When looking for an ideal location for a cell site, engineers involved in radio frequency design look at the surrounding typography, population, and traffic density of a given area.

Signaler on the roof

Once a location is chosen, carriers must get clearance from municipality and zoning commissions. They then negotiate leasing terms with building landlords for every individual site. Currently, Sprint has 38,000 sites across the U.S.

The subtle antenna

At this location, Sprint has installed three antennas on the roof. The range of each antenna depends on its location. For a site like this, this antenna is estimated to cover about a quarter square mile.

The other for 800MHz

Below that is the RF amplifier for the 800MHz band. By installing the radio heads directly below the antenna (instead of nearby underground or at the cell site's base station, both of which are common methods), the carrier minimizes the amount of lost signal.

Color-coded labeling

Cords that run throughout the antenna and the radio heads are wrapped in bright tape, with different colors representing different network speeds and bands. It helps engineers to quickly identify fiber optics for 4G LTE and 3G CDMA technology.

Fiber back haul station

Data from the base station is fed through this fiber back haul station, which will then send signals through AT&T's (the incumbent cable company in the City) fiber cables. The signals travel about 10 miles out to Brisbane, Calif., where calls and Internet receptions are routed to the appropriate locations.

Aging technology

Next to Sprint's new base station is one of the carrier's own previous, 15-year-old base station (left), which is equipped with radio heads inside. To the right of it are two backup battery sources. The station only provides 1X, 3G, and voice technology, and will soon be decommissioned.